Conventionally, with the development of wireless communication technologies, there are known technologies for broadening communication bands by combining a plurality of antennas between a mobile station and a base station. As such a technology, MIMO (Multiple Input Multiple Output) is employed in HSPA+ (High Speed Packet Access Plus) and LTE (Long Term Evolution). MIMO is a technology for achieving broadband wireless communication in such a manner that a base station simultaneously transmits different data to a mobile station through a plurality of antennas, and the mobile station receives the data through the antennas and combines the received data. Some mobile stations are capable of expanding a communication-enabled area, some are capable of switching a plurality of different frequency bands (for example, 2 GHz and 800 MHz) to respond to a change in communication environment. Some of such mobile stations have a plurality of antennas for respective frequency bands (a total of four antennas) so as to allow MIMO communication in each frequency band.    Patent document 1: Japanese Laid-open Patent Publication No. 2010-74760    Patent document 2: Japanese Laid-open Patent Publication No. 2010-50936
The above-described mobile station has two antennas (a main branch and a sub branch) for each of two systems with respect to each frequency band. These branches are composed of RF (Radio Frequency) components; the RF components are preferably few in number from the standpoint of small footprint on the mobile station or reduction of power consumption. Furthermore, depending on an RF component, a characteristic of one branch (the sub branch) may be degraded in a particular frequency band. Especially, an operation region of an RF component is narrow in a low-frequency band of about 800 MHz; therefore, this tendency is prominent in the low-frequency band. In consideration of such circumstances, an RF component for a sub branch in a particular frequency band (for example, 800 MHz) is sometimes not implemented in a mobile station. However, as such a mobile station does not implement the RF component used for application of the MIMO technology, the mobile station does not properly perform separation, demodulation/decoding, and error correction of data received from a base station, and as a result, the above-described MIMO technology may not be applied to the mobile station.